HTTP servers usually operate at port 80. Yet NAT routers as most are these days assign port to outgoing requests so they would know when request is returned that which computer connected to it, it's suppose to be. They do it cause they can only use one public IP even though all computers behind router are given public IP address they are local IP address. Meaning they only work for everyone behind that router.
So how does server handles this. It only works at port 80, and router sends at whatever ports it wishes to do based on what is available and how it is programmed.
Computer A to router. 126.96.36.199.22:80
Router to World: 188.8.131.52.102:1 -ISP given IP address:Port to distinguish between computers connected to it.
Or maybe there is a difference between port and source port.